1. Field of the Invention
This invention relates to a method of manufacturing a pair of or more rotational members such as a male shell and a female shell, for example, lens barrel units.
2. Related Background Art
In a unit shell comprising a pair of male shell and female shell which is used in a camera lens barrel, optical accuracy and physical accuracy such as moderate operation weight are required when the male shell and the female shell are repeatedly moved relative to each other. For the structure of parts for satisfying these requirements, it is necessary to form a minute gap between the male shell and the female shell.
As a method of forming such gap in manufacturing a unit shell comprising a pair of male shell and female shell by a molding process, there has heretofore been adopted a method of utilizing the molding contraction of resin as disclosed in U.S. Pat. No. 4,115,505. It comprises making in advance a female shell which is an outer shell, and then mounting and holding the female shell in a shaping mold for a male shell which is an inner shell, thereafter pouring resin into the mold to thereby form the male shell, thus manufacturing a unit shell comprising a pair of male and female shells. In this case, the male shell molding-contracts, whereby a minute gap is formed between the male shell and the female shell. Such prior art, however, has suffered from the following disadvantages.
Firstly, as long as an attempt is made to create a gap by utilizing molding contraction, the procedure of molding a male shell on the basis of a female shell is unavoidable. That is, the male shell is formed of a resin material and a metal material cannot be used for the male shell. Therefore, it has been unreasonable to apply the prior art to a male shell which requires strength of the member itself, such as a thin-walled and long male shell indicated by 1 in FIG. 1 of the accompanying drawings or a short-diametered and elongated male shell indicated by 1 in FIG. 9 of the accompanying drawings.
Secondly, when an attempt is made to make a female shell by resin molding, undercutting of the bore of a female shell indicated by 12a in FIG. 2 of the accompanying drawings becomes necessary. The undercutting process, as is known, requires the provision of a mechanism for pulling out a mold member 12 by rotating it or pulling out the mold member 12 by mechanically contracting it in the direction of its center axis. These mechanisms complicate the structure of the mold and it has been unavoidable that the manufacture of the mold requires much labor and the mold becomes expensive.
Thirdly, there is a case where the undercutting process is limited to the processing by the contraction of the mold member. It is a case where the undercut of the bore of the female shell is not of a screw-like shape but has grooves axis-symmetrical with respect to the center axis of the shell. In this case, dimensions having taken into account the mold space for providing therein a complicated mechanism called contraction are required of the bore of the female shell. This has limited the attempt to reduce the dimensions of the undercut bore of the female shell as well as the design the product. Further, a camera's lens barrel having a male side barrel for holding a lens optical system, etc. and a female side barrel mating with the male side barrel, characterized in that a cylindrical portion is formed and welded by a soluble or grindable resin material at one end of the female side barrel made of a metal material or a resin material, and then the female side barrel in which said cylindrical portion has been formed and welded is used as a jig for molding together with said cylindrical portion to pour the resin material of the male side barrel into the cylindrical portion and the interior of the female side barrel and thereby mold the male side barrel, whereafter said cylindrical portion is removed by dissolution or grinding and the female side barrel is mated with the male side barrel is known from Japanese Patent Application Laid-Open No. 8508/1982.
The method of making the lens barrel disclosed in the above-mentioned patent application includes the step of forming the cylindrical portion of a soluble or grindable resin material, and this leads to the complication of the structure of the mold and the structure of the molding material.